The following describes a conventional DVD-Video disc (hereinafter referred to as a “DVD”).
FIG. 1 is a diagram showing the structure of a DVD. As shown at the bottom of FIG. 1, the DVD includes a logical address space in between the lead-in area and the lead-out area. In the logical address space, volume information for the file system is stored at the top, and application data such as video and audio is stored in the subsequent areas.
The file system of the DVD is a file system compliant with ISO9660 and the Universal Disc Format (UDF). The file system is a mechanism for representing data on a disc by units called directories and files. In a personal computer (PC), a file system called FAT or NTFS is used. This kind of file system allows a computer to process data recorded in the hard disk in the form of directories and files. Usability is thereby enhanced.
Both UDF and ISO9660 are used in DVDs as their file systems. UDF and ISO9660 are sometimes referred to collectively as “UDF Bridge”. Data recorded on a DVD can be read out by the file system driver of either UDF or ISO9660. Of course, for DVD-RAM/R/RW, which are rewritable DVDs, data reading, writing and deletion are physically possible via the file systems.
Data recorded on a DVD exists as directories or files as shown in the upper left of FIG. 1 via the file system. A directory called “VIDEO_TS” is placed immediately below the root directory (“ROOT” in FIG. 1), where application data for the DVD is recorded. The application data is divided and recorded as plural files. The following are some of the major files.
VIDEO_TS.IFO A disk reproduction control information file
VTS—01—0.IFO Video title set #1 reproduction control information file
VTS—01—0.VOB Video title set #1 stream file
. . . . .
Two extensions are prescribed. “IFO” is an extension which indicates that a file with this extension stores reproduction control information. “VOB” is an extension indicating that a file with this extension stores an MPEG stream, which is AV data. The reproduction control information is information that includes information for implementing interactivity (techniques for dynamically changing the reproduction state according to a user operation) used by the DVD, as well as information that is attached to a title or an AV stream, such as meta data. The reproduction control information in the DVD is generally called navigation information.
The reproduction control information files include “VIDEO_TS. IFO”, which manages the entire disc, and “VTS—01—0.IFO” which is reproduction control information for individual video title sets. “01” in the body of the filename indicates the number of the video title set. For example, when the number in a video title set is #2, the filename of the video title set is “VTS—02—0.IFO”. Note that a single DVD can store plural titles, that is, plural movies with different content and plural movies with the same content, but which have different versions.
The upper right of FIG. 1 shows a DVD navigation space in the application layer of the DVD, i.e., a logical structure space where the reproduction control information mentioned above is expanded. Information in “VIDEO_TS.IFO” is shown in the DVD navigation space as Video Manager Information (VMGI). The reproduction control information, which exists for each video title set, such as “VTS—01—0.IFO”, is shown in the DVD navigation space as Video Title Set Information (VTSI).
Program Chain Information (PGCI), which is information about a reproduction sequence called a Program Chain (PGC), is described in VTSI. The PGCI is made up of groups of cells and a kind of programming information called a command. Each cell represents partial or whole segments in a Video Object (VOB; MPEG stream). Cell reproduction means reproducing segments in a VOB that are specified by the cell.
Commands are processed by a DVD-capable virtual machine and are similar to a Java (registered trademark) Script executed in a browser. Java (registered trademark) Script performs window and browser controls (for example, opens a new browser window), in addition to logical operations. Meanwhile, a DVD command performs only reproduction control for AV titles (for example, the specification of a chapter to be reproduced), in addition to logical operations. This is a difference between a DVD command and Java (registered trademark) Script.
Each cell includes information about the start address and end address (logical recording address on the disc) of a VOB recorded on the disc. A player reads out data using information described in the cell concerning the start address and end address of the VOB, and reproduces the read out data.
FIG. 2 is a diagram for describing the navigation information in the AV stream. The interactivity which is characteristic to DVDs is not implemented by the navigation information alone recorded in the above-described “VIDEO_TS.IFO” and “VTS—01—0.IFO” and so on. Several pieces of important information for realizing interactivity are multiplexed in the VOB with video data and audio data, using dedicated carriers called navigation packs (hereinafter referred to as “navi pack(s)” or “NV_PCK”).
Here, a description is given of a menu as a simple example of interactivity. Several buttons appear on the menu screen. For each of the buttons, the details of a process to be performed when the button is pressed are defined. One button is selected on the menu. Highlighting, which is a semitransparent image to be overlaid on the selected button, indicates to the user that the button on which it is overlaid is being selected. The user can shift the highlighting to any of the buttons located above, below, right or left of the currently selected button, using the Up/Down/Right/Left key on the remote control. Using the Up/Down/Right/Left key on the remote control, the user shifts the highlight to a button corresponding to the process the user wishes to execute, and then presses the Determination key. Accordingly, a program for the command corresponding to the selected button is executed. For example, the reproduction of a title or a chapter is executed by a command (for example, refer to Japanese Laid-Open Patent application No. 09-282848).
The upper left of FIG. 2 shows an overview of the control information stored in NV_PCK.
NV_PCK includes highlight color information and button information for each button and so on. Color palette information is described in the highlight color information. The color palette information specifies a semitransparent color for a highlight to be overlaid. Within the button information, the following information is described: rectangular area information, i.e. information about the position of each button; shift information indicating a shift from one button to another button (specification of a destination button corresponding to the user selecting one of the Up/Down/Right/Left keys on the remote control); and button command information (a command to be executed when the button is selected).
As shown in the upper right center of FIG. 2, a highlight on the menu is created as an overlay image. The overlay image is an image generated by giving a color specified by the color palette information to a button specified by the rectangular area information in the button information. The overlay image is displayed on the screen, superimposed on the background image shown on the right of FIG. 2.
The menu of the DVD is displayed in the above-described manner. In order to allow menu information to be dynamically updated in synchronization with the stream, a part of the navigation data is embedded in the stream using the NV_PCK. This is done for example, to allow the menu to be displayed for only five to ten minutes during movie reproduction. A second reason is to allow the stream and the menu information to be displayed in synchronization with each other even for application data, for which synchronous display of the stream and menu information is difficult. Another major reason is to improve user.operability. For example, by storing, in NV_PCK, information for supporting special reproduction, it becomes possible to smoothly decode and reproduce AV data stored on a DVD even when the AV data is reproduced in a special manner such as fast forward and rewind reproduction.
FIG. 3 is a diagram that shows an image of a VOB, which is a DVD stream. Types of data such as video data, audio data, and subtitle data shown in FIG. 3(A) are each packetized and packed, as shown in FIG. 3(B), based on the MPEG system standard (ISO/IEC13818-1), and multiplexed respectively as shown in FIG. 3(C) to be generated as a single MPEG program stream. NV_PCK, which includes a button command for realizing interactivity, is multiplexed together with the packets and the packs.
Data multiplexing in the MPEG system is characterized in that, while each data to be multiplexed forms a bit string based on the decoding order, data to be multiplexed, i.e., video data, audio data and subtitle data is not necessarily arranged in the order of reproduction, i.e., decoding order. This is attributable to the fact that a decoder model for MPEG system streams (generally referred to as a “System Target Decoder” or an “STD” (refer to FIG. 3(D)) has decoder buffers corresponding to the respective elementary streams obtained by demultiplexing the multiplexed data, and the demultiplexed data are temporarily stored in the respective decoder buffers until the time of decoding. The size of decoder buffers specified by the DVD-Video standard differs per elementary stream. The size of the buffer for video data is 232 KB, the size of the buffer for audio data is 4 KB, and the size of the buffer for subtitle data is 52 KB.
In other words, the subtitle data that is multiplexed together with the video data is not necessarily decoded or reproduced with the same timing as the timing with which the video data is decoded and reproduced.    [Patent Reference 1] Japanese Laid-Open Patent Application No. 9-282848